Two-step method for developing silver halide emulsion film

ABSTRACT

PARTICULAR DEVELOPMENT ACCELERATORS AND INHIBITORS ARE USED WITH KNOWN DEVELOPING AGENTS OF THE HYDROQUINONE TYPE IN A TWO-STEP DEVELOPMENT OF SILVER HALIDE EMULSION FILMS TO IMPROVE DENSITY AND CONTRAST IN THE SHADOW AND MIDTONE AREAS, TO EXTEND USEFUL LINEAR RANGE IN THE HIGHLIGHT AREA AND TO ENHANCE THRESHOLD SENSITIVITY. THE CHARACTERISTIC DENSITY-LOG EXPOSURE CURVE PRODUCED BY THIS METHOD HAS A DUAL GAMMA. THE DEVELOPER EMPLOYED IN THE FIRST STEP CONTAINS A POLYETHYLENE GLYCOL ACCELERATOR, AND PREFERABLY THE DEVELOPER EMPLOYED IN THE SECOND STEP CONTAINS A POLYETHOXYLATED QUATERNARY AMMONIUM SALT AS AN ACCELERATOR AND NITROBENZIMIDAZOLE NITRATE AS AN INHIBITOR.

Z. REYES June 19, 1973 TWO-STEP METHOD FOR DEVELOPING SILVER HALIDE EMULSION FILM Filed Oct. 1971 FIEI l cue v55 0F fXAMPL 5 L6 2.0 LOG EXPOSURE FIEI E IE IEI 3I cuevss 0F EXAMPLE 1.6- LOG EXPOSURE United States Patent Olfice 3,740,227 Patented June 19, 1973 3,740,227 TWO-STEP METHOD FOR DEVELOPING SILVER HALIDE EMULSION FILM Zoila Reyes, Menlo Park, Calif., assignor to Stanford Research Institute, Menlo Park, Calif. Filed Oct. 15, 1971, Ser. No. 189,695 Int. Cl. G03c 5/30 US. Cl. 96-663 5 Claims ABSTRACT OF THE DISCLOSURE Particular development accelerators and inhibitors are used with known developing agents of the hydroquinone type in a two-step development of silver halide emulsion films to improve density and contrast in the shadow and midtone areas, to extend useful linear range in the highlight area and to enhance threshold sensitivity. The characteristic density-log exposure curve produced by this method has a dual gamma. The developer employed in the first step contains a polyethylene glycol accelerator, and preferably the developer employed in the second step contains a polyethoxylated quaternary ammonium salt as an accelerator and nitrobenzimidazole nitrate as an inhibitor.

The invention herein described was made in the course of or under a contract with the Air Force Avionics Laboratory.

SUMMARY OF THE INVENTION This invention relates to a two-step method of developing silver halide emulsion films. The process is one in which the film is treated first, by tank or spray method, with a developer of the phenidone-hydroquinone type which contains a polyethylene glycol additive as an accelerator. Following this step, the partially developed film, either with or without being given an intermediate short-stop Wash, is treated with a second developer of the hydroquinone type. The latter developer in one embodiment of the invention preferably contains a polyethoxylated quaternary ammonium salt as well as 6- nitrobenzimidazole nitrate. In another preferred embodiment of the invention, the latter nitrate compound is incorporated in a short-stop wash employed between the developing steps. For convenience of description, these several developing and wash solutions, whether employed in bath or spray methods of operation, will be referred to herein as the first developing bath the short-stop bath and the second developing bath.

A practice of the present invention provides a number of advantages. Thus, it tends to increase the density and improve the contrast in the shadow and midtone exposure regions. Further, it extends the linear range in the highlight area by reducing density and contrast therein. The process permits compensation for overexposure and underexposure of the film, thereby enhancing the latitude and effective speed, or threshold sensitivity, of the silver halide emulsion. The density-log exposure curves resulting from the controlled development process of this invention are characterized by What is termed a dual gamma, or dual contrast range, response. Specifically, the slope of the (lower) portions of the curve in the shadow-midtone region has a somewhat greater value than does that of the upper portion of the curve. This decreased slope of the upper portion of the curve, when compared with that of a control curve, is a manifestation of the reduced density and contrast which the present invention brings about in this highlight area.

The first developing bath is one of the hydroquinonephenidone type which, in addition to the usual additives present in a developing bath, also contains polyethylene glycol. In this bath the content of the hydroquinone (pdihydroxybenzene) may range from about 0.75 to 10 g. per liter of the aqueous developer solution. The content of phenidone (l-phen'yl 3 pyrazolidone) typically ranges from about 0.75 to 2.5 g. per gram of hydroquinone, and a typical bath will contain equimolar proportions of these constituents, e.g., 1.1 g. hydroquinone and 1.62 g. phenidone, per liter of solution. The content of the polyethylene glycol can range from about 0.5 to 1.5 g. per gram of phenidone. The polyethylene glycol material is one having an average molecular Weight of from about 600 to 3,000, with materials of from about 900 to 2,000 average molecular weight being preferred. This glycol component is effective in that it acts to promote the activity of the phenidone and thus to enhance development in the shadow area. At the same time, development by the hydroquinone is somewhat retarded, thus restricting development in areas of high exposure.

In addition to the foregoing constituents, the first developing bath Will typically contain an alkali such as caustic soda, sodium carbonate, Kodalk (sodium metaborate) or borax -(frequently employed along with boric acid to butfer the solution at the desired alkaline pH); a perservative and development controller such as sodium sulfite, usually present in the amount of from about 25 to g. per liter; and an anti-fogging retarder, usually potassium bromide, present in an amount of about 0.3 to 10 g. per liter.

The short-stop bath, when employed, quickly checks the action of the developer on the sensitive layer by neutralizing the alkali. This bath is normally an aqueous solution of acetic acid having a pH of from about 4 to 5.5. In lieu of the acetic acid, the short-stop bath may contain other acidic materials such as sodium bisulfite, sodium metabisulfite or monosodium citrate. Gel hardeners may also be employed in this bath if desired. In one embodiment of this invention, this bath also contains from about 10 to 50 mg. of 6-nitrobenzimidazole nitrate per liter of bath solution. When the developing process includes the use, between the developing steps, of a shortstop bath containing this nitrate compound, then the succeeding, second developing bath can be one of the phenidone-hydroquinone of Metol-hydroquinone character, as hereinafter described.

The second developing bath is one of the phenidonehydroquinone or Metol-hydroquinone type. Here, however, when phenidone is employed it should be used in an amount of from about 0.02 to 0.1 g. per gram of hydroquinone, an amount which is significantly less than the ratio used in the first developing bath. When Metol is used, it should preferably be employed in amounts of about 0.1 to 0.75 g. per gram of hydroquinone. This second developing bath will also contain conventional alkali, sulphite and bromide components, all as recited above in connection with the description of the first developing bath. Additionally, in those development operations wherein between the first and second developing steps there is not employed a short-stop bath containing 6-nitrobenzirnidazole nitrate, the second developing bath preferably contains from about 0.05 to 0.3 g. of a polyethoxylated quaternary ammonium salt and from about 5 to 30 mg. of the 6-nitro-benzirnidazole nitrate compound per liter of developing solution. The quaternary ammonium salt, wherein the normal accelerating action of the salt is greatly moderated by the presence of the ethylene oxide substituent, is one having the general formula where R represents a higher alkyl group such as one as derived from oleic acid, stearic acid or coco fatty acid,

while x and y represent integers which total from about 2 to 15. Compounds of this character, which are herein referred to as higher alkyl polyethoxylated quaternary ammonium salts are manufactured and sold by the Armour Industrial Chemical Company, a division of Armour and Company, Chicago, 111., under the trademarks Ethoquad C/ 12, Ethoquad C/ 25, Ethoquad /12, Ethoquad 18/ 12, Ethoquad 18/25. In these Ethoquad compounds, the first number or letter of the code designates the source of the higher alkyl radical indicated by an R in the above formula (18=stearic acid, C=coco fatty, and O=oleic acid), while the second numbers 12 and 25 of the code represent compounds having a total of 2 and 15 moles of ethylene oxide, respectively.

The present invention is adapted to be used in either tank or spray methods of development, and with a wide variety of films and film use applications. Among the latter are aerial photography, X-ray films, laser photography and all application of films in holography including extension of information storage, vibration analysis, interferometry, contour mapping and fiow visualization.

In the examples given below, the film employed is Kodak Aerial Films 3404 and all test strips of this film are given a 10- second exposure through a calibrated step wedge in a Mark VI sensitometer with a 3-line viriable area filter plus a 0.6 neutral density filter (Wratten No. 96). Absolute log E=7.6710. This sensitometer is a product of E G & G, Inc., Bedford Mass. For each test strip so obtained there is prepared a characteristic curve :by measuring the density of each step and then drawing a graph with the densities on the ordinate and the log exposures on the abscissa.

The processing temperature for both tank and spray development tests, as described below in the examples, was 20 C. Development times varied with the type of development, tank or spray, and with the composition of the developing solutions under evaluation. Generally a short-stop bath and/or a running water rinse were used between the first and second developments. Other steps or processing cycles were the same as those used for the D-19 and Ethol 90 controls which were processed as follows:

D-19 control Tank development Spray development;

Developer- 8 minutes minutes. SS bath 30 seconds 20 seconds. Fixing bath 4 minutes 2 minutes. Final wash 10 minutes 4 minutes.

In the case of Ethol 90 control, the processing conditions were the same except that the tank development time was 3 minutes and the spray development time was 2 minutes and a water wash was used instead of the SS bath.

The composition of the D-19 control, a Kodak product, is as follows:

Water (125 F. or 52 C.) cc 500 Metol (or Elon) g 2.2 Sodium sulfite, desiccated g 96.0 I-Iydroquinone g 8.8 Sodium carbonate (monohydrated) g.. 56.0 Potassium bromide g 5.0

Add cold water to make 1 liter.

for use as a second developing bath (and which is identified herein as PQ-llB) has the composition:

Warm water t cc 750 Sodium sulfite, desiccated g 100 Hydroquinone g 5.0 Phenidone g 0.2 Potassium bromide g 1.0 Kodalk g 10.0 Ethoquad C/12 g 0.5 6-nitrobenzimidazole nitrate g 0.01

Add cold water to make 1 liter.

A composition which is well adapted for use as the first developing solution -(and which is identified herein as PQ-2) has the composition:

Add cold water to make 1 liter.

The following examples illustrate the invention, but are not to be construed as limiting:

Example 1 In this operation, the film which has been exposed in the manner described above is developed by the tank method using PQ-2 after the first developing bath and Ethol as the second developing bath. The following processing cycle is employed:

PQ-2 minutes 2 SS bath seconds 30 Running water rinse do 30 Ethol 90 dev. minutes 2 Running water rinse seconds 30 Fixing bath --rninutes-.. 4 Final wash do 10 The characteristic curve of the emulsion obtained in this test is presented (as Curve la) in FIG. 1 of the drawing where, for comparison, there are also presented characteristic curves as obtained using 'only the D-19 control (Curve lb), the Ethol 90 control (Curve Ic) and the curve resulting from inverting the development order, with Ethol 90 being followed by PQ-2 (Curve Id). In this latter case, the first development step took 6 minutes and the second developing step 1 minute. The characteristic curve (Ia) obtained for strips processed in PQ-2/ Ethol 90, 2 min./ 2 min. had a dual gamma of the desired character. The steeper toe-tomidrange gamma is 1.7 and that of the highlight area is 0.8. The base plug fog value of 0.15 is very low and the /2 gamma speed of 4.9 based on first gamma is high compared with 2.4 for 13-19 developer.

Example 2 The process cycle set forth in Example 1 is followed except that the times in the PQ-2 and Ethol 90 developers are 6 minutes and 1 minute. Further, the shortstop bath (SS) employed contains 0.001 percent 6-nitrobenzimidazole nitrate. The characteristic curve of this emulsion is shown in FIG. 1 as Curve II. The values for the gamma in this dual gamma curve are 1.7 and 1.2. The base plus fog density is 0.23 and the half gamma speed is 4.6.

Example 3 In this operation, the film, exposed in the manner described above, was developed by the spray method using PQ-2 as the first developing material and Ethol 90 as the second developing material. The following processing cycle was used:

PQ-2 minutes 2 SS Washing seconds Water rinse "do..-" 15 Ethol 90 do 45 Water rinse do 15 Fixing bath minutes 2 Final wash do 4 The characteristic curve which was obtained in this test is presented (as Curve 111(1) of FIG. 2 of the drawings where, for comparison, there are also presented characteristic curves as obtained using only the D-l9 control (Curve 1111)) and the Ethol 90 control (Curve IIIc). It will be seen that the densities of the shadows and low midtone areas of Curve Illa are well above those of the D-l9 and Ethol 90 controls. The densities of the upper midtones are close to or slightly below those of these controls, while the densities of the highlights are Well below those of the controls. The values for the gammas in Curve IIIa are 1.7 and 1.2. The base plug fog value is 0.16 and the /2 gamma speed is 4.3.

Example IV The process cycle set forth in Example 3 is repeated except that the second developer employed is PQ-l 1B rather than Ethol 90, and the time of the second developing step is lengthened to 2 minutes. The characteristic curve of this emulsion, which also exhibits the dual gamma effect, is shown in FIG. 3 as Curve IVa. For the sake of comparison there is shown as Curve IV!) the characteristic curve using the D-19 control alone. It will be seen that the densities of Curve IVa are well above those of Curve IVb over all except the highlight range. The Values for the gammas in Curve IVa are 1.9 and 1.1. The base plus fog value is 0.20 and /2 gamma speed is 0.45.

I claim:

1. The process of developing a silver halide emulsion film to provide a film having a characteristic density-log exposure curve manifesting dual gamma characteristics,

said process comprising subjecting the film to a two-step development sequence in which the first developing bath is a hydroquinone-phenidone developer which contains a polyethylene glycol material having an average molecular weight of from about 600 to 3,000, the phenidone being present in an amount of from about 0.75 to 2.5 g. per gram of hydroquinone and the glycol material being present in the amount of from about 0.5 to 1.5 g. per gram of phenidone, and

in which the second developing bath is a hydroquinone developer which contains from about 0.02 to 0.1 g. of phenidone or from about 0.1 to 0.75 g. of Metol, per gram of hydroquinone.

2. The process of claim 1 wherein the second developing bath also contains from about 0.05 to 0.3 g. of a higher alkyl polyethoxylated quaternary ammonium salt and from about 5 to 30 mg. of 6-nitrobenzimidazole nitrate per liter of said developing bath.

3. The process of claim 1 wherein between the developing steps there is employed a short-stop bath containing from about 10 to mg. of 6-nitrobenzimidazole nitrate per liter of the short-stop bath solution.

4. The process of claim 1 wherein the first developing bath contains from about 0.75 to 10 g. of hydroquinone per liter of the developing bath.

5. The process of claim 4 wherein the second developing bath is D-19.

References Cited 

